Hydraulic power source provided with cooling means



y 1960 M. M. SCHUSTER 2,946,203

HYDRAULIC POWER SOURCE PROVIDED WITH COOLING MEANS Filed Aug. 26, 1957 INVENTOR. MICHAEL M. ScHUsTER Arron/MY ite Tttes HYDRAULIC POWER SOURCE PROVIDED WITH COOLING MEANS Filed Aug. 26, 1957, Ser. No. 680,223

6 Claims. (Cl. 62396) This invention relates to a hydraulic power supply which delivers hydraulic fluid under pressure.

For the operation of hydraulically actuated tools such as pullers for setting tubular blind rivets, hydraulic pressures of the order of several thousand pounds per square inch are required. The operation of boosting the pressure heats the fluid, often by as much as 70 F. When this fluid is provided to a hand-held tool for actuating the tool, the tool is also heated. It is obvious that a handheld tool which is heated to a temperature which is 70 F. above ambient cannot be held barehanded by an operator.

In addition, various parts of the pumps and tools are made with different materials that have different coefficients of expansion. A large temperature rise may cause the parts to stick unless they are fitted so loosely at normal temperatures that the pump is extremely inefficient over a wide range of temperatures.

Because of the intermittent nature of the demand for fluid in many tools, it is advantageous to use equipment such as pumps and the like which are of a minimtun size, and which can develop the required pressure in an accumulator over an extended period of time. This desirable usage of minimum design components is hindered by effects which occur as the result of heating of the hydraulic fluid as a consequence of its being put under pressure. For example, cavitation effects often occur in the pump when the hydraulic fluid becomes heated, and in order to deliver the necessary pressure and volume it has been found necessary to utilize larger components to compensate for these effects than would be necessary if the hydraulic fluid were kept cool. All of the above considerations illustrate the need for keeping the temperature of the hydraulic fluid low. On the other hand, it is economically unsound to provide a separate refrigeration system which exists solely for the purpose of cooling hydraulic fluid to avoid the above defects.

It is an object of this invention to provide a hydraulic power source which includes means for cooling the hydraulic fluid which cooling means do not require apparatus in addition to that which is needed for pressurizing the hydraulic fluid.

In the practice of this invention, a pump is provided which receives fluid to be pressurized from a reservoir, and delivers it under pressure to a system where the fluid is to be used. Gas-actuated power means are supplied for driving the pump which are preferably, although not necessarily, of the differential piston type for providing a boost in pressure for the fluid over the pressure of the gas used to operate the power means. Cycling means are provided which alternately connect said power means to a source of pressurized gas and then to a cooling conduit. The cooling conduit is immersed in hydraulic fluid contained in the reservoir, and expansion of the gas from the power means after it has performed its work of driving the pump causes a cooling effect in the cooling conduit which cools the hydraulic 2,946,208 Patented July 26, 1960 ice fluid which is to be supplied to the pump, thereby keeping the temperature of the pumped hydraulic fluid at a suitably low temperature and reducing or eliminating adverse effects which result from pumping the fluid at high temperatures. This is accomplished, of course, by providing cooler fluid to be pressurized. While the total temperature rise may be the same, the final temperature of the pressurized fluid will be lower than if the cooling were not provided.

The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, of which:

Fig. 1 is a side view partly in cross-section showing a hydraulic power source according to this invention in one operating condition;

Fig. 2 is a cross-section taken at line 2-2 of Fig. 1; Fig. 3 is a cross-section taken at line 3-3 of Fig. 1; and

Fig. 4 shows a position of an element of Fig. 1 which causes the power source to assume another operating condition.

In Fig. 1 there is shown a hydraulic power supply according to this invention. A pump 10 has an inlet 11 and an outlet 12 provided with check valves 13 and 14, respectively. Inlet 11 is connected through check valve 13 and conduit 15 to outlet 16 of a reservoir 17. The reservoir contains hydraulic fluid 18 to be pressurized and supplied to a working system.

The outlet 12 of the pump 10 is connected through check valve 14 to supply conduit 19, which in turn is connected to a hydraulic accumulator 20. In accordance with standard constructions this accumulator may conveniently include a piston 21 within a cylinder 22, said piston being loaded by gas pressure admitted through valve 23 in the cylinder wall. The well known diaphragm type accumulator could be used instead of the pistoncylinder type. A conduit 24 departs from the accumulator to supply pressurized hydraulic fluid to any desired working tool.

The pump iii includes a pump cylinder 25 and a piston 26 which is reciprocable in cylinder 25. The piston is driven by gas-actuated power means which power means comprises a diaphragm 27 having a central rigid portion 28 of greater cross section than the piston 26. A flexible portion 29 of the diaphragm which is clamped between two shell halves 30, 31 joins the wall of the shell to the rigid portion of the diaphragm. The, lower shell half is vented by vent 32. The region between shell half 30 and the diaphragm 27 comprises a working chamber 33 to which a working fluid such as compressed air can be admitted through a conduit 34.

Conduit 34 interconnects working chamber 33 to a cycling means 35. This cycling means may conveniently comprise a selector valve which may be actuated by any desired means (not shown). For example, the cycling means could be linked to the diaphragm or the piston 26 so as to be actuated by movement of these elements. Working fluid is supplied to the cycling means from a pressure source 36 which may be a simple compressor, or any source of air, such as a shop air line. The pressure source connects to an inlet 37 of the cycling means. The selector valve is connected to a cooling conduit 38 at its outlet 39. It will be seen that the cycling means 35 has three connections, its inlet being connected to the pressure source, its outlet being connected to the cooling conduit, and its third opening being connected to conduit 34. A rotatable valve element 40 in the cycling means has a right-angle passage 41 therein which can selectively interconnect either conduit 34 and inlet 37, or conduit 34 and outlet 39.

A portion of the cooling conduit 38 is at least partially immersed in fluid 18 in the reservoir, and after passing through the portion of the cooling conduit in the reservoir, the exhaust working fluid is discharged to atmosphere.

The operation of the system should be evident from the drawing and the above description. A pumping cycle is begun by turning the cycling means to the position shown in Fig. 1. By this means, compressed gas is admitted to working chamber 33. The gas causes diaphragm 27 to move down, and piston 26 forces fluid con t-ained in pump cylinder 25 out through valve 14 and into conduit 19. At the end of this pumping stroke, the cycling means are turned to the position shown in Fig. 4. Then the compressed gas in the working chamber (which will be substantially at the same pressure as its source 36) exhausts through the conduit 34, into the cooling conduit 33, and out to atmosphere. The pressure of the gas in the working chamber thereby drops from the pressure of the source to atmospheric, and expands accordingly. Expansion of the gas from the working chamber to the atmosphere results in a temperature drop in the cooling conduit. The cooling conduit is in heat transfer relationship with the hydraulic fluid in reservoir 17, and thereby cools the fluid. This drop in pressure in the working chamber allows the diaphragm to move upward, which movement maybe assisted by springs 42, 43 which may be provided for that purpose, if desired. Springs 42 and 43 are sometimes referred to as a return means. This movement represents an intake stroke wherein fluid from the reservoir flows through inlet 11 into the pump cylinder 25, from which it is expelled in the next pumping stroke of the pump.

Self-cycling booster pumps, of the diiferential area type are well known, and many of them provide for interconnection between the diaphragm or some other unit which is responsive to the piston position for purpose of actuating the cycling means, thereby providing a self cycling pump. On the other hand, it is equally possible to operate this cycling means by hand or by any other desired means, for example from a unit responsive to a low system pressure, or from an entirely unrelated timer or other control means.

The pump is a booster pump utilizing a differential area between'the area of the piston 26 and diaphragm 27 to boost pressures. The output hydraulic pressure relative to atmosphere is inversely proportional to the ratio of the areas of the diaphragm and piston 26, and is directly proportional to the pressure of the gas source.

It will be understood that other types of gas-actuated pumps may be used, which may or may not provide a boost to the hydraulic pressure over the gas pressure, and which may or may not use a diaphragm construction. A simple differential piston pump is a variation of the diaphragm pump, which may also be used. The essence of this invention is to utilize a gas-actuated power means wherein the expansion from the working chamber 33 passing through a cooling conduit acts to cool the hydraulic fluid which is to be pressurized.

In the operation of this device in setting blind rivets by the use of hydraulic tool, it has been found that instead of a 5070 F. rise in the temperature of the hydraulic fluid over room temperatures, the rise is ordinarily kept to within a 10 F. rise above normal temperatures. The differential temperature rise is about the same, but by starting the fluid at a cooler temperature, the fluid remains in a temperature range where unfavorable results from pumping hot fluid do not occur. this is a decrease in cavitation, and an increase in the efficiency of the power unit as a whole. In addition, the gas used for operating the power unit is easily secured from shop sources and serves to cool the hydraulic fluid without requiring any auxiliary equipment. Except for an extension of the cooling conduit, all equipment needed for this invention is also needed for hydraulic pumping.

This invention is not to be limited by the embodiment shown in the drawings and described in the description The result of which is given by way of illustration and not of limitation, but only in accordance with the scope of the. appended claims.

I claim:

1. A hydraulic power s pply comprising: a pump having an inlet and an outlet; a reservoir for containing liquid to be pressurized by said pump; conduit means interconnecting said reservoir and said pump inlet for supplying liquid to said pump; gas-actuated power means connected to said pump for operating the pump, said gasactuated power means being adapted to be moved in a first direction by gas pressure, and in a second direction opposite to the first; return means for moving the gasactuated power means in the second direction; a cooling conduit disposed at least partially within said reservoir and adapted to be at least partially submerged in liquid in said reservoir; cycling means including a cycling means inlet adapted to be connected to a source of gas under pressure, a cycling means outlet connected to said cooling conduit, and a connection to said gas-actuated power means, said cooling conduit exhausting to a lower pressure than said source of gas under pressure; whereby said pump is operated by connecting said power means to said source of gas under pressure by connecting the connection and cycling means inlet to move the gasactuated power means in one of said directions, and then connecting said power means to the cooling conduit by connecting the connection and the cycling means outlet, enabling the return means to move the gasactuated power means in the other direction, thereby operating the pump through one cycle, expansion of gas from the power means into said cooling conduit serving to reduce the temperature of the liquid contained in the reservoir and in contact with said cooling conduit.

2. Apparatus according to claim 1 in which the pump and power means comprise a piston device actuable by gas under pressure.

3. Apparatus according to claim 1 in which the power means and the pump comprise a unitary differential area pump for boosting pressure of the hydraulic fluid above the pressure of the gas from said source.

4. Apparatus according to claim 1 in which said power means and pump are unitary and comprise a single structure, said pump including a piston and a cylinder, and said power means including a diaphragm having a larger area than said pistonand afixed to said piston for moving the piston as a consequence of gas pressure exerted against said diaphragm.

5. Apparatus according to claim 4 in which the cycling means comprises a selector valve adapted to selectively interconnect the source to said power means, and the power means to said exhaust conduit.

6. A hydraulic power supply comprising: a combined pump and power source, said pump comprising a pump cylinder and a pump piston, said cylinder having an inlet and an outlet, said power meanscomprising a diaphragm of larger area than said piston, said diaphragm being attached to said piston for reciprocating the same, an enclosure above said diaphragm for creating a working chamber between said enclosure and said diaphragm for receiving gas under pressure for moving said diaphragm; spring means on the other side of said diaphragm from the working chamber; cycling means comprising a selector valve having an inlet, an outlet, and a connection, said connection being in fluid communication with said working chamber; a source of gas under pressure connected to said inlet; and a cooling conduit connected to said outlet; a hydraulic reservoir discharging into the cylinder inlet, the cooling conduit being disposed at least partially in the reservoir, and adapted to be at least partially submerged in liquid in said reservoir, whereby, when the selector valve connects the gas source to the working chamber through the said connection, the diaphragm and pump piston are driven so as to force hydraulic fluid out of the pump 5 cylinder into a hydraulic system under pressure, and when the selector valve interconnects the working chamber and the cooling conduit through the connection, the spring serving to move the diaphragm into the working chamber, so that the piston moves so as to draw liquid into the pump cylinder to be pressurized, and gas from the working chamber flows into the cooling conduit and cools the conduit which in turn cools liquid in the reservoir by thermal heat transfer.

Reterences in the of this patent UNETED STATES PATENTS 515,585 Hill Feb. 27, 1894 2,033,210 Tennant et al. Mar. 10, 1936 2,518,246 Morris Aug. 8, 1950 FOREIGN PATENTS 1,090,677 France Apr. 1, 1955 

